This invention relates generally to the processing of video data, and, more specifically, to stabilization of moving images acquired by a camera or other video acquisition device that is subject to unintentional shaking.
The holding or movement of a camera by hand during the taking of a series of video frames without shakes or jitters is quite difficult, particularly when the camera is very small and light. The trend is for the size of both digital still cameras having the ability to take short film clips and video motion picture cameras, such as camcorders, to be made smaller and lighter. Video image sequences are also taken by mobile phones and portable digital assistants (PDAs), which are also very small. The resulting shaking results in recording moving images that are very irritating to watch, being most noticeable in scenes that do not include large movements of objects in them. It is therefore desirable to compensate in some manner for this and other undesired camera motion.
One class of image stabilizing cameras contains a pair of very small gyroscopes mounted within the camera with their axes perpendicular to each other. When the camera moves, the gyroscopes offer resistance to the movement and produce force vectors in a direction opposite to that of the camera's motion. An electrical control signal proportional to these force vectors is used to compensate for random and/or cyclic movements of the camera while acquiring image frames, thereby to stabilize the images. This can be done either mechanically or electronically. Mechanically, the optical axis of the camera may be moved to reposition the image projected onto the sensor in a direction opposite to that of the camera shake. Movement of a gimbal mounted camera lens is often used to perform this repositioning. The sensor may alternatively be moved by the stabilization signal. Electrically, the camera may contain a processing circuit that is responsive to the stabilization signal to shift the output of the image sensor both horizontally and vertically, in order that the image remains stable over multiple frames.
Other image stabilization techniques, which do not require the use of gyroscopes or any other mechanical reference, detect global (overall) movement of the image between two successive frames as part of the signal compensation. The later acquired image is then electronically repositioned to eliminate movement caused by camera shaking. These techniques are most commonly implemented by separately adding to a camera a motion estimation capability that is dedicated to image stabilization.